240 Inheritance of Tight and Loose Paleae in Oats 



Y = a fjictor capable of rendering some of the paleae on the plant 

 pure tight. 



Z = a factor capable of rendering some of the paleae on the plant 

 more or less sclerotised but never wholly tight. 



It follows that all pure tight forms must be homozygous for X, no 

 matter whether they contain Y or Z, separately or together, or not. 

 Similarly all plants which never throw pure tights, i.e. all " nuda " 

 forms, must be recessive for X. They, too, may or may not contain 

 X and Y. Now let any two individuals of these two classes be crossed. 

 It is evident that quite a number of F^ combinations may result : 



XYZ • xYZ\ 



Xyz • xyz 

 XYz • xyz 

 XYZ xyz } 



are a few. 



One feature will alone be constant : the heterozygosity of X. All, 

 therefore, will throw one-quarter pure tights in the F^ generation. 

 This is consonant with our proven results. Now if in the F^ combi- 

 nation the presence of one dose of X determine that, say, x °/^ of the 

 paleae shall be pure tight, then it is not unnatural to infer that the 

 remainder will be variably tightened and hardbacked according as 

 Y and Z are present both homozygously, both heterozygously, one 

 homozygously and one heterozygously, and so on, or both absent. 



It should be added that the functions assigned to the factors Y and Z 

 are, of course, merely hypothetical. Just as possibly either or both 

 may have some negative, inhibiting action, thus lowering the basic x °/^ 

 of pure tight grains in the F^ plant (cf Plant B in Table II), while 

 quite possibly they may govern the number of grains per spikelet and 

 thus have an indirect influence on the hardening of the paleae. For 

 it has been noted that progressive tightening of the paleae always 

 reduces the number of flowers in a spikelet, until, in the pure tight 

 forms, the repulsion between the many-flowered habit and tightness of 

 paleae is complete. 



Some further light is cast on the complex nature of the various 

 " nuda " types in Table V ; but admittedly it is only a glimmer. A few 

 interesting points, however, stand out. The results of two seasons' 

 plantings are contained in the table, as, owing to the tediousness of 

 the classification, with its careful scrutiny of every palea, only a limited 

 number could be undertaken at one time. In 1916 the parents were 

 simply single panicles rubbed out and called " various nuda forms " ; 



